The Prehospital Index (PHI) is a triage-oriented trauma severity scoring system comprising four components: systolic blood pressure, pulse, respiratory status, and level of consciousness, each scored 0 to 5. The PHI was developed after analysis of 313 cases to provide an objective prehospital scoring system for distinguishing less seriously injured patients (minor trauma) from those patients who are likely to die within 72 hours after injury or who require general or neurosurgical operative intervention within 24 hours (major trauma). A PHI of 0 to 3 indicated minor trauma, and a PHI of 4 to 20 signified major trauma. Retrospective analysis of an additional 465 consecutive trauma cases revealed that patients with a PHI of 0 to 3 (minor trauma) had a 0% mortality and a 2% rate of general or neurosurgical operative intervention. Those with a PHI of 4 to 20 (major trauma) carried a 16.4% mortality and an emergency operative rate of 49.1%. The PHI was applied prospectively to 388 consecutive trauma cases presenting to the Butterworth Hospital Emergency Department from October through December 1984. Of the 351 patients scored as minor trauma in the field, there was a 0% mortality and only a 0.3% operative rate. Those scored as major trauma in the field had a mortality of 27% (PHI 4 to 7, 0%; PHI 8 to 20, 53%) and an operative rate of 40.5% (PHI 4 to 7, 22%; PHI 8 to 20, 57.9%). These data demonstrate the ability of the PHI to predict mortality (P less than .001) and the need for emergency general or neurosurgical operative intervention (P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)